(a) Technical Field
The present invention relates to a charging control method and system for an environmentally friendly vehicle. More particularly, the present invention relates to a charging control method and system that enhances charging efficiency by improving a power control method of a power factor correction (ITC) converter while a battery is being charged through an on board charger (OBC) in a plug-in hybrid electric vehicle (HEV) or an electric vehicle (EV).
(b) Background Art
As known in the art, a green vehicle (e.g., an environmentally friendly vehicle) such as a plug-in hybrid electric vehicle (HEV) or an electric vehicle (EV) uses an alternating current (AC) electric vehicle supply equipment (EVSE) in connection with a distribution system to charge a battery thereof. In addition, an on board charger (OBC) is built in the plug-in HEV or EV to charge the battery by connecting the vehicle to the AC EVSE.
FIG. 1 is an exemplary diagram illustrating main components of an OBC built in a vehicle 200 according to the related art. As shown in FIG. 1, the OBC includes a power factor correction (PFC) converter 210 that converts an AC input voltage Vac of an AC power source 100 into a direct current (DC) voltage Vdc and simultaneously compensates for the power factor of the voltage, and a DC-DC converter 220 connected between the PFC converter 210 and a high-voltage battery 230 to convert the DC voltage output from the PFC converter 210. In the example shown in FIG. 1, the PFC converter 210 is operated as a boost converter to convert the AC input voltage Vac applied from the AC power source 100 into the DC voltage Vdc at the outside of the vehicle 200. The DC-DC converter 220 may be an insulated DC-DC converter that employs a full-bridge (FB) or half-bridge (HB) switching circuit.
Meanwhile, as the concept of charging energy is introduced to the fuel consumption rate (e.g., miles per gallon equivalent (MPGe)), i.e., the power ratio of the plug-in HEY or EV, the importance for power transmission efficiency of the OBC built in the vehicle is increased.
In the plug-in HEY or EV, the high-voltage battery 230 as a power source for driving the vehicle is operated in a wide voltage range based on the charging/discharging amount thereof, and it is an important subject to achieve high efficiency in the entire voltage range. In addition, the voltage of the battery 230 connected to an output stage of the DC-DC converter 220 of the OBC is determined based on a charging state, and the variation of the voltage of the battery 230 is substantial when the battery 230 is charged. Conventionally, it was difficult to achieve high efficiency in the entire voltage range. In the related art, a method has been developed of controlling the output voltage Vdc of the PFC converter 210 to be a fixed voltage in the OBC shown in FIG. 1.
FIGS. 2a and 2c are exemplary diagrams illustrating a charging control method of the battery in the vehicle through the OBC. FIG. 2(a) illustrates a state of the output voltage Vdc of the PFC converter during the charging of the battery in the related art. FIG. 2(b) illustrates an effective duty Deff for controlling the output voltage of the DC-DC converter during the charging of the battery. FIG. 2(c) illustrates a state of the battery voltage Vbat during the charging of the battery.
As shown in FIG. 2, in the related art charging control method, the output voltage Vdc of the PFC converter is controlled to be constantly fixed. In particular, the variation in the battery voltage is substantial, and therefore, high efficiency may not be achieved in the entire voltage range. The average charging efficiency of the OBC is lowered in a wide operation range of the battery voltage. As a result, the MPGe of the vehicle may deteriorate and the charging time of the vehicle may increase, due to the lowering of the average charging efficiency.